Natural diversity - LIB magazine

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Same-sex penguin parents, dominant female clownfish, and a snail with two sexes: An open-minded look at nature reveals that there is no norm outside of diversity. Learn about how Darwin’s traditional worldview still continues to shape biology, and why queer perspectives enrich the research of biodiversity.

Ariolimax dolichophallus, the banana slug, has enjoyed celebrity status for over thirty years following its cameo in Quentin Tarantino’s 1994 film “Pulp Fiction” with lead actor John Travolta wearing a UC Santa Cruz T-shirt that featured the bright yellow slug. The banana slug was named the mascot of the University of California, whose campus is at the heart of its habitat, the Redwood Forest, in 1986. Behavioural ecologist Professor Mariella Herberstein also focuses on the Ariolimax. “This slug offers a particularly good example of how diverse nature can be. It has female and male reproductive organs at the same time, enabling it to mate with same-sex partners,” says Herberstein, deputy director general at the LIB. “Biodiversity comprises more than just the diversity of species. Researchers need to broaden their minds to include all dimensions of diversity to fully understand biodiversity,” Herberstein adds.

Diversity is the norm

Diversity in terms of sex, reproduction, and sexual behaviour is a fundamental aspect of biological systems, rather than merely an exception, in nature. Some penguin species engage in same-sex social parenting. Bonobos use same-sex sexual activity to strengthen social bonds within a group. Male seahorses carry their offspring in a brood pouch on their abdomen until birth. Clownfish are able to change sex during their lifetimes. Herberstein explains: “A female clownfish will share a group of anemones with several males. She is the largest and most dominant individual and thus the leader of the group. Following the female’s death, the strongest male will take over and begin to turn into a female in the course of more than a year.”

Outdated role models

The last twenty years have finally allowed us to take such observations seriously in biology rather than categorising them as exceptions or “unnatural” occurrences. The worldview of naturalist Charles Darwin, as presented in his 1871 work “The Descent of Man, and Selection in Relation to Sex,” characterised the approach for nearly a century before that. Herberstein explains: “Darwin assigned to males and females in the animal kingdom strict gender roles. Males were supposed to be active, dominant, and polygamous, while females were passive, shy, and monogamous.” Research conducted by evolutionary biologist Professor Geoff Parker in the 1970s and later showed that the females of many animal species selectively mate with a number of males. Queen bees, for example, will mate with up to twelve drones in their nuptial flights. Evolutionary biologist Professor Dr Marlene Zuk explained based on her research on the mating behaviours of insects in the 2000s that our ideas about “male” and “female” behaviours in nature were primarily based on assumptions made following the pattern of human gender stereotypes.

"We need to look at the animal world with an open mind to learn to perceive behaviours in a more nuanced manner."

Prof Dr Mariella Herberstein

Non-valuing terminology

To this day, Herberstein, who researches spiders, continues to notice an anthropocentric view of animals that is often unconsciously shaped by cultural influences. “The dominant female behaviour in the ‘black widow’ spider is often described using particularly bloodthirsty language even though aggressive fights are actually quite rare.” Herberstein strives to use the most neutral terminology possible in her publications.
“I avoid words such as ‘harem’ or ‘virgin’. They are human concepts applied to the animal world that will only serve to perpetuate stereotypes.”
Herberstein also points out that her analysis of textbooks in the English language has shown that explanations of gender and sexual behaviour are often quite simplified in them.
“Any non-binary person sitting in such a lecture will necessarily feel excluded and probably won’t stay in biology for too long.” Herberstein hopes to see more diversity in research and in the museum going forward. She says: “Queer perspectives can break through the walls of the binary approach. We need to look at the animal world with an open mind to learn to perceive behaviours in a more nuanced manner. Diversity is always enriching, but we do need to recognise it first.”

Natural diversity in LIB research projects

Beneficial inflammations

The development of abdominal brooding in ricefish from the Indonesian island of Sulawesi is the research focus pursued by LIB evolutionary biologist Dr Julia Schwarzer. She studies inflammation with beneficial effects and a unique tissue that has revolutionised reproduction even beyond ricefish. The diversity of Sulawesi ricefish has always fascinated Julia Schwarzer, evolutionary biologist and head of the Evolutionary Genomics section at the LIB. “Some ricefish shed their eggs after spawning, while others carry them connected by thread-like filaments, anchored to the abdomen by a unique tissue until they hatch.” This “plug” forms after spawning, is supplied with blood, and will not detach before hatching. Schwarzer and her team investigated its formation with the help of anatomical and genetic analyses of the two Oryzias and Adrianichthys ricefish lineages, discovering that cells and signalling pathways involved in formation of this tissue are actually responsible for controlling inflammatory responses. “The fact that inflammation comes with great innovative power as well was an important finding,” says Schwarzer.

They discovered that cells and signalling pathways that actually control inflammatory reactions were involved in the development of the tissue. "The fact that inflammation also has great innovative power is an important finding," says Schwarzer. Her research also discovered a similarity between the development of the ricefish plug and the mammalian placenta. Both have particular genes activated. An inflammatory immune response plays a key role in the evolution of both ricefish and humans. Her research group is now planning to continue its work to understand the formation of the “plug” on single-cell level.

Diverse record holders

African cichlids exhibit a great diversity of sex chromosomes and rapid adaptation skills. They even include one species that is able to self-fertilise. Evolutionary biologist Dr Astrid Böhne, head of the comparative genomics department at the LIB, has studied cichlids and sex chromosomes for more than 15 years. Teaming up with a colleague who brought back a cichlid of the genus Benitochromis from Cameroon, she discovered that “it reproduced in spite of living isolated in its aquarium.” Since it had not had any opportunity to mate with another fish, she completed full genome sequencing and discovered that the fish had self-fertilised. She pursued some other projects to investigate the evolution of sex chromosomes in African cichlids, primarily in Lake Tanganyika.

Analysing the entire genome and active genes of 240 species with a focus on differences between females and males, Böhne and her team uncovered a great diversity of sex chromosomes in more than 70 species. These chromosomes adapted extremely frequently during the evolution of these fish. Böhne explains: “These cichlids are a prime example of the rapid emergence of numerous new species. They currently hold the record for sex chromosome changes among vertebrates.” Further research is underway to determine the precise influence of sex chromosomes on species formation.